Many devices have been proposed for infusing medical solutions to patients. Although these devices may be specifically engineered to optimized some particular aspect or feature of the infusion process, and thus be designed to function in quite different ways, their basic objective is the same. Namely, each device is intended to infuse fluids to a patient at an effectively constant rate over a specified interval of time to achieve volumetric accuracy in a sustained operation.
It will be appreciated that IV infusion therapy may be appropriate for various purposes in a wide variety of situations. Further, although many IV patients are bedridden, it may not always be necessary for the patient to remain lying down during infusion therapy. Indeed, but for limitations imposed by the infusion device being used, there may be no need for the patient to remain nonambulatory for the prolonged periods of time that may be necessary for the therapy. Accordingly, some IV devices have been specifically engineered and designed for use by ambulatory patients.
To be effective, operational IV infusion devices which can be carried by ambulatory patients need to satisfy several specific requirements. First, the device should be light weight and be easily carried by the patient. Further, the device should be simple to operate and easy to use. Additionally, the simplicity of the device will, hopefully, permit complete operation by the patient without assitance from medical staff personnel. Importantly, the device must operate within selected operational parameters which will ensure sufficient infusion accuracy to properly treat the particular ailment of the patient.
In order to reduce weight requirements, several IV infusion devices intended for use by ambulatory patients have avoided incorporating electronic components. Instead, they have relied on purely mechanical means for infusing fluids to the patient. One method is, of course, to rely on gravity to infuse fluids into the patient. A gravity means, however, can be cumbersome for the ambulatory patient. Alternatively, a stored energy device, such as a spring, may be used to impart a positive mechanical force on the fluid being infused. Perhaps more efficiently, such a positive force may be generated with an elastomeric material sucha as latex. These elastomeric materials are relatively light weight when compared with spring loaded devices and, accordingly, have some appeal. It happens, however, that the force which is generated by a stretched elastomeric material is substantially constant throughout only a part of the range of stretch given to the material. For operation outside this range, there is a nonlinear variable force response from the material which can cause an erratic pumping operation. Since it is desirable to have a constant force applied to the fluid, in order to maintain predictable fluid flow, if an elastomeric material is used to provide the impelling force for an IV infusion device it is preferable that the elastomeric material remain stretched in that part of the range of stretch where a substantially constant force results. Further, in order to avoid additional unpredictable nonlinearities, it is desirable that the elastomeric material providing the impelling force be stretched equally over the area of material generating the force.
In light of the above, it is an object of the present invention to provide a disposable IV infusion device for use by an ambulatory patient which uses an elastomeric material that is maintained in a stretched state during sustained operation to infuse fluids with a substantially constant force on the fluid. Another object of the present invention is to provide a disposable IV infusion device for use by an ambulatory patient which is light weight and easy to carry. Still another object of the present invention is to provide an IV infusion device for use by an ambulatory patient which is simple to operate and maintain and which can be reused if desired. Yet another object of the present invention is to provide an IV infusion device for use by an ambulatory patient which is relatively easy to manufacture and comparatively cost effective.